From insects to mammals, olfactory receptor neurons (ORNs) expressing the same odorant receptors converge their axonal projections to specific glomerular targets in the antennal lobe/olfactory bulb, creating an odor map in these first olfactory structures of the central nervous system. In the fruit fly Drosophila, antennal lobe projection neurons (PNs, equivalent to vertebrate mitral/tufted cells) send dendrites to glomeruli and synapse with ORN axons; PN axons then relay the olfactory information to higher brain centers the mushroom body and the lateral horn. Over the past five years and thanks to the support of the previous grant, we have made significant progress towards understanding how wiring specificity in the Drosophila olfactory circuit is established, both in terms of cellular and developmental events and their molecular mechanisms. In this renewal, we propose a series of molecular, genetic and biochemical experiments to continue our effort in understanding the mechanisms by which each PN or ORN chooses one of 50 alternative areas to target its dendrites or axons, ultimately resulting in the formation of a stereotyped and highly precise circuit for flies to sense and discriminate odors and pheromones. We utilize both candidate gene approaches and forward genetic screen to identify molecules that are required for these targeting processes, and then investigate their detailed mechanisms of action. Emphasis will be placed on studying ligands and receptors that guide PN dendrites and ORN axons to appropriate areas in the antennal lobe and faciliate their synaptic matching. We expect that completion of the proposed experiments in this grant will significantly enrich and expand our understanding of the logic and mechanisms of olfactory circuit assembly. These studies will contribute to our understanding of a number of important neurobiological questions, including neuronal fate specification, dendritic guidance and targeting, and the logic of the assembly of the olfactory circuits and neural circuits in general. Our studies will also provide insight into how olfactory information is transferred and transformed along the central pathways. PUBLIC HEALTH RELEVANCE Understanding how neural circuits are wired during normal development is a prerequisite for understanding the nature of pathological wiring, which underlie many human neurological and psychiatric disorders. In addition, knowledge of insect olfactory system organization and development can be used to help design strategies to combat malaria, transmitted by mosquitos that utilize primarily olfaction to find their mates and human host.